Combination linear and rotary vibration damper



ZEMQM my 4X9 i950 a. E. @'cwwn COMBINATION LINEAR AN ROTARY VIBRATIN DAMPER Filed 31m@ IW, 1947 Patented July 4, 1950 COMBINATION LINEAR AND ROTARY VIBRATION DAMPER Bernard E. OConnor, Buffalo, N. Y., assgnor to Houdaille-Hershey Corporation, Detroit, Mich., a corporation of Michigan Application June 17, 1947, Serial No. 755,180

3 Claims.

This invention relates to improvements in the damping of linear and rotary vibrations and more especially where such vibrations are liable to occur in the same mass.

Insofar as the applicant is advised, the problem of damping the vibrations in what may be termed a free mass, such as an aerodynamic surface, of which airplane wings or tail surfaces are examples, has heretofore defied successful solution. Conventional shock absorbers cannot be used with such a mass because there is nothing to serve as a base to which the shock absorber can be anchored. Moreover, such a free mass is subject not only to torsional vibrations, but also to linear' vibrations. The damping of either of these modes of vibration does not necessarily stop the other inode of vibration.

Flutter in aerodynamic surface structures is a self-excited vibration due to the association oi various categories of freedom, such as lexural and torsional, with the energy supplied by the airstream while an aircraft is in motion, and more especially while in iiight. All aerodynamic surfaces may be referred to as unstable systems, because when displaced from equilibrium position their tendency is to iiutter with ever-increasing amplitude. All aerodynamic surfaces become unstable above respective determinable speeds.

A principal object of the present invention is to provide for the damping of both linear and torsional modes of vibration, such as flutter in aerodynamic surfaces, in a simple, inexpensive and efective manner.

T t is another object of the invention to provide a combinational torsional and linear vibration damper utilizing a free inertia mass.

A further object of the invention is to provide a new and improved vibration damper including a rotary and linearly movable vibration damping mass.

Still another object is to increase the stability of aerodynamic surfaces, and more particularly to enable vsuch surfaces to be operated at greater air speeds.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, wherein:

Figure l is a fragmentary more or less schematic plan view of an airplane wing incorporating the present invention;

Figure 2 is an enlarged more or less schematic sectional view through the vibration damper shown in Figure l and taken substantially on the line II-II; and

Figure 3 is a horizontal sectional View taken substantially on the line III-III of Figure 2.

As an example of a mass which is subject to both linear and torsional vibrations, an aerodynamic surface structure, such as an airplane wing IQ, is shown in Figure l. Both the wings and the tail surfaces of airplanes are subject to linear and torsional modes of vibration. The association of these two modes with the airstream as a source of energy will at certain speeds result in instability which manifests itself in the form of iiutter. Many cases of structural failure have been attributed to flutter. This instability can be rendered substantially stable by coupling an auxiliary damping mass effective in both linear and torsional modes of vibration to the main mass through a viscous medium or through a viscous and a spring ymedium. Any means which will render stable otherwise unstable aerodynamic surfaces permits higher speeds for a given structure or lighter structures for a given speed and is therefore an important and valuable expedient.

According to the present invention, both linear and torsional vibrations are dampened through the medium of an inertia member which resists sudden deviations from a state of equilibrium or from a static condition with respect to its supporting structure. The inertia member is supported in a manner to be relatively movable or to permit movement relative thereto of the supporting structure.

In a representative embodiment, a damper unit H is provided which is adapted for use with the aerodynamic member or wing l!) and, as shown in Figure l, is adapted to be applied to the wing at the locus of approximately maximum potential flutter, as at the tip and preferably on the torsional axis thereof.

The unit Il comprises a casing l2 providing a chamber or housing for a weight or inertia member i3. The casing I2 may be of any preferred construction and the inertia member I3 may be made from any preferred material and in its simplest form comprises a metal disl; of suitable diameter and thickness.

The relationship of the casing l2 and the inertia member I3 is such that they are relatively movable linearly and torsionally or rotatably. In the specic embodiment illustrated, substantial relative rotary movement is permitted and linear movement is substantially restrained to a path only in directly opposite directions for the reason that the unit H is especially adapted for use with an aerodynamic member. However. it will be understood that where desirablethe chamber within the casing I2 may be so proportioned that the inertia member I3 will be free for relative linear movement in any or all directions.

In an airplane wing or similar 'aerodynamic surface, the linear vibrations are, of course, up and down. For this purpose, the casing i2 is so proportioned with respect to the diameter of the inertia member I3 that clearance is afforded for substantial relative vertical movement of casing and inertia member, but the inertia member is conned against substantial horizontal movement, this being primarily to conserve space.

. Accordingly, the vertical internal dimension of the casing I2 is such as to aiord substantial clear-` ance for vertical movement of the inertia member I3. The horizontal dimension on the diameter of the inertia member i3 is only slightly greater than the diameter of the inertia member.

Axially of the inertia member i3, the internal dimension of the casing I2 is only slightly greater than the thickness of the inertia member so as to aiord a closely spaced relationship between the opposing side surfaces f .the inertia member and the side walls of the chamber aiiorded by the casing I2.

Means are provided for supporting the inertia member i3 in a preferably vertically centered normal or equilibrium relation within the casing I2 but permitting relative vertical movement between the casing and inertia member. Herein such means. comprises a pair of generally U shaped leaf springs I4, each connected at one leg to the casing I2 as by means of a rivet I5 and to the weight I3 at the other leg as by means of a screw I6 in such a manner that the inertia member I3 is maintained in substantially uniform spaced relation to the upper and lower walls of the casing I2. For balanced support the springs I4 are preferably directed in respectively opposite directions.

The chamber provided by the interior of the casing I2 is substantially filled with a viscous fluid i'I such as silicone which will aiord resistance to either linear or rotary motion of the inertia member I3 with respect to the housing l2. This resistance is caused by the shear resistance of the .viscous film in the small clearances between the closely opposing surfaces of the casing and inertia member and particularly between the relatively broad opposing surfaces at the two sides of the inertia member I3 and the sides of the casing I2, and is proportional to the relative velocity between the inertia member I3 and the casing I2.

Through this arrangement, the inertia member I3 is adapted for relative vertical or rotary movement in the casing I2 as permitted by yielding of the springs I4 and resistance of the fluid friction. After any displacement, the springs Il tend to equalize the position of the inertia member I3 within the chamber I2.

Since the spacing between the side faces of the inertia member I3 and the opposing walls of the casing I2 is quite close, the iilm of viscous uid in the spaces aiords substantial viscous shear lm resistance to any relative movement of the casing and the inertia member. This resistance to relative movement is valuable in damping vibrations since it tends to hold the casing I2 against any quick movements either oscillatory or linear relative to the inertia member I3 which, due to the inertia of its mass, resists following Such vibratory movements. As a result, vibrations in the mass with which the vibration damping unit is associated, such as the airplane wing it, are eectively dampened. 0n the other hand, ordinary movements oi the airplane wing or other mass to be dampened with which the damping unit il is associated are in no way interfered with. With an airplane wing or other aerodynamic surface this is of particular importance since interference with necessary maneuvers of the aerodynamic surface must be avoided.

For accommodating expansion of the viscous uid Il, a suitable air space may be left in the top of the damper chamber l2, as indicated at l.

In order to maintain the viscosity of the uid il of substantially uniform viscosity in spite oi great variations in external temperatures, and especially where very low temperatures may prevail as in high altitude flying, temperature regulating means may be provided in or for the damper unit I i. In a simple form such regulating means may comprise an electric heating element l and a thermostatic or like control 2G. Preferably a separate temperature or viscosityvregulator is provided for the virtually separate masses of fluid in both the upper and the lower sections oi the unit i i.

It will, of course, be understood that various details may be varied through a wide range without departing from the principles of this invention, and it is, therefore, not the purpose to limit the patent granted hereon other-wise than necessitated by the scope of the appended claims.

I claim as my invention:

1. In combination in a vibration damper of the character described, a circular iiat inertia mass and means for movably supporting the inertia mass including an enclosure defining a chamber having spaced straight parallel Walls in closely spaced relation to the sides of the inertia mass and other spaced straight, parallel walls normal to said first mentioned walls and disposed in close relation to diametrically opposite portions of the periphery of the inertia mass, additional walls of the enclosure chamber being substantially spaced from the periphery of the inertia mass of from a line joining said diametrically opposite portions, and viscous iiuid in the chamber restrained in displacement from one part of the chamber to the other part by the close spacing between said sides and said opposite peripheral portions of the inertia mass and the respective chamber walls disposed in opposition thereto.

2. In `combination in a vibration damper of the character described, a circular fiat inertia mass and means for movably supporting the inertia mass including an enclosure defining a chamber having spaced straight parallel walls in closely spaced relation to the sides of the inertia mass and other spaced straight parallel walls normal to said first mentioned walls and disposed in close relation to diametrically opposite portions of the periphery of the inertia mass, additional walls of the enclosure chamber being substantially spaced from the periphery of the inertia mass 90 from a line adjoining said diametrically opposite portions, viscous uid in the chamber restrained in displacement from one part of the chamber to the other part by the close spacing between said sides and said opposite peripheral portions of the inertia mass and the respective chamber walls disposed in opposition thereto, and respective generally U-shape spring members normally maintaining the inertia mass in substantially center relation between said additional walls of thechamber, said spring members each having 5 one leg secured to the adjacent periphery of the inertia mass and the remaining leg secured to the enclosure and with the mouths of the spring Us opening in respective opposite directions.

3. In combination in a vibration damper,

means defining a closed chamber, a circular in ertia mass within said chamber, the circular inertia mass having opposing flat sides and the chamber being dened by ilat surfaces in closely spaced relation to the sides of the inertia mass, opposite peripheral portions of the inertia mass being substantially spaced from opposing walls of the chamber, the chamber having additional opposed straight parallel walls in closely spaced relation to diametrically opposite portions of the periphery of the inertia mass disposed 90 from the rst mentioned peripheral portions, means yieldably supporting the inertia mass in peripherally spaced relation to both of said rst mentioned walls of the chamber, and a viscous uid in the chamber providing lms having shear resistance. to relative parallel movement between said dat sides and said dat surfaces for resisting linear and relative rotary movements of the inertia mass within the chamber, and also providing a 25 body of fluid in each of the substantial spaces between the inertia mass and said rst mentioned chamber walls.

BERNARD E. OCONNOR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 989,958 Frahm Apr. 18, 1911 1,766,995 Hofmann June 24, 1930 2,038,603 Roche Apr. 28, 1936 2,139,817 Gogan Dec. 13, 1938 2,180,893 Best Nov. 21, 1939 2,271,976 Hasbrouck, Jr., et al. Feb. 3, 1942 FOREIGN PATENTS 20V Number Country Date 337,466 Great Britain Nov. 3, 1930 508,513 Great Britain July 3, 1939 515,318 Great Britain Dec. 1, 1939 518,291 Great Britain Feb. 22, 1940 726,544 France Mar. '7, 1932 

